1. Field of the Invention
The present invention relates to a differential pressure sensor. More particularly, the present invention provides a differential pressure sensor with an improved sensitivity and structure system.
2. Description of the Related Art
There are known differential pressure sensors, that is, devices capable of sensing the difference in pressure between two points of a circuit containing a fluid (liquid, gas, vapor, etc) under pressure and to provide an output signal, typically electric, representing this difference. Typically, such devices are used to sense the pressure difference between two points respectively downstream and upstream of an element in a circuit under pressure, such as an oil filter.
Differential pressure transmitters of (hereinafter also only ‘transmitters’) are differential pressure sensors capable of sensing a plurality, typically a continuum, of values of the aforesaid pressure difference within a working interval. In this respect they differ from differential pressure sensors of the ON/OFF type (commonly called ‘electrical or electromechanical differential’ sensors), capable only of sensing whether a threshold pressure difference has been reached.
One class of transmitters, characterized by a complex structure and high industrial costs, separately senses the value of the two pressures, which are subsequently compared in order to provide the output signal representing their difference.
Another class of transmitters directly senses the pressure difference, the output signal being a function of that value, and typically proportional thereto.
The latter type of transmitter typically comprises a piston fluctuating inside a cylinder, the piston dividing the cylinder into two chambers in which the fluid has substantially the same pressure, respectively, as the aforesaid two points in the circuit being monitored. The piston is subject to an axial force, the modulus of whose resultant is a function of the pressure difference, and the position of the piston inside the cylinder depends on the axial force and on an elastic axial force exerted by a spring interposed between the piston and the cylinder.
The piston comprises, at an end axial thereof, a magnet which is facing a bottom wall of the cylinder. In proximity to the face opposite the bottom wall (typically in contact with the opposite face) there is a magnetic sensor (for example a Hall effect sensor) which enables a continuous sensing of the distance of the magnet from the bottom wall. A suitable electronic circuit translates the information produced by the magnetic sensor into a signal representing the pressure difference.
According to the Applicant the differential pressure sensors of the prior art are not free of drawbacks. According to the Applicant, for example, there is a problem related to the positioning of the magnetic sensor in proximity to the aforesaid bottom wall. Such positioning must in fact be sufficiently precise, axially and/or radially, and stable over time while simultaneously ensuring that the magnetic sensor is not subjected to excessive mechanical stresses. This task is made even more difficult by the fact that if the magnetic sensor is mounted on an electronic card, the latter will typically be produced with geometric tolerances that conflict with the desired tolerances for the positioning of the magnetic sensor.
Accordingly, there is a need for an improved differential pressure sensor that addresses at least one of the concerns noted above.